1. Field of the Invention
The invention pertains to internal combustion engines and, more specifically, to camshafts with drive elements, bearing elements, and cam elements.
2. Description of the Related Art
Many different possibilities have been disclosed in the prior art for securing camshaft elements to a carrier shaft in a rotationally fixed relationship. Special methods include widening of a hollow shaft in the region of the camshaft elements that have a nonround insertion opening (European Patent Disclosures EP-A 190 841, EP-A 282 166, EP-A 303 845, EP-A 389 070); sintering the powdered-metal cam elements onto the shaft (EP-A 364 028); inserting corrugated tension sleeves between a longitudinally fluted carrier shaft and the cam element that also has a fluted insertion opening (EP-A 745 757); firmly gluing the cam elements to a longitudinally fluted carrier shaft (EP-A 119 112); circumferentially fluted regions on the carrier shaft, which are deformed by the camshaft elements (EP-A 486 876, EP-A 521 354); firmly screwing the camshaft elements to the carrier shaft (PCT publication WO-A 93/10336); firmly clamping or wedging the camshaft elements to the carrier shaft (EP-A 170 187, EP-A 178 536, EP-A 178 537), and so forth.
By means of what is known as variable valve control, it is possible to successfully optimize the various given conditions for the wide speed (rpm) and load range of an internal combustion engine.
The concept of variable valve control allows varying both the opening and closing times of the individual valves and their stroke. Along with rotating the entire camshaft or individual cam elements, it is also known to displace either the entire camshaft (EP-A 108 238, EP-A 116 306, EP-A 590 577), or individual cam elements (U.S. Pat. Nos. 5,359,970, 4,730,588, and 5,158,049), or intermediate members (French patent disclosure FR 26 94 786) in the longitudinal direction of the camshaft. In U.S. Pat. No. 5,359,970, for example, the displaceable cam elements have a protrusion profile, but have the same base circle radius as the axially nondisplaceable cam elements. Each displaceable cam element is urged in the displacement direction and rests with the larger cam region on an intermediate member that forms a stop. Upon attaining the base circle region it is axially displaced so that the existing nondisplaceable cam element is functionally disconnected. The displacement is effected by means of a sleeve that is displaceable on the camshaft and can be acted upon hydraulically, and the restoration is effected via a spring surrounding the camshaft and supported on the nondisplaceable cam element.